Outbreaks of two deadly viruses captured the world’s attention in 2013, but neither turned into the global pandemic expected to strike one of these years.

One of the viruses, known as MERS, causes Middle East respiratory syndrome. The other, H7N9, is a new bird flu virus from China. Each virus has infected fewer than 200 people, but both kill a sizable number of the people who contract them. Although the viruses have not spread far from where they started, the scientific effort to decipher and combat them has had global reach.

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